This proposal addresses a new approach to cancer treatment that may allow for selective killing of tumor cells regardless of their proliferative status, with potential for fully destroying the tumor. This approach is based on our functional genomic study that revealed that the expression of C0PZ2, a gene encoding a subunit of the coatomer protein complex I (COPI) is drastically decreased in the majority of the tested tumor cell lines and in human cancer tissues. The loss of C0PZ2 expression is a corollary of tumor-specific downregulation of a tumor-suppressive miRNA, miR-152. As a result of miR-152/COPZ2 downregulation, tumor cells become dependent on COPZ1, a gene that encodes an isoform of C0PZ2. While normal C0PZ2-expressing cells survive COPZ1 depletion, C0PZ2-deficient tumor cells are killed by COPZ1 knockdown. Cell death induced by COPZ1 inhibition is associated with Golgi fragmentation and, in contrast to the effects of almost all the anticancer drugs, is independent of cell proliferation. Hence, COPZ1-targeting therapy of miR152-deficient tumors has the potential for eradicating all the cancer cells in the body. We propose a set of specific aims to delineate the tumor-promoting effects of miR-152 down regulation and the frequency of miR-152/COPZ2 silencing in clinical cancers, and to investigate the potential toxicity of COPZ1 inhibition and the feasibility of targeting COPZ1 with small molecules. In Aim 1, we will identify target genes of miR-152 and analyze their effects on tumor progression. In Aim 2, we will analyze expression of COPZ1, C0PZ2, miR-152 and miR-152 target genes in clinical samples of malignant melanoma and prostate cancer. In Aim 3, we will generate mice with homozygous or heterozygous knockout of COPZ1 to determine the deleterious effects of COPZ1 depletion. We will also develop and test prototype COPZ1-targeting small molecules through rational drug design. The success of this project will elucidate the spectrum and properties of miR-152-deficient tumors and provide proof of principle for the eradication of such tumors through therapeutic targeting of COPZ1.